Phase Shifts in the Oscillatory Interlayer Exchange Coupling across Cu Layers

The dependence of the phase of the oscillatory exchange coupling between ferromagnetic (FM) layers across fcc Cu on the composition of the ferromagnetic layer has been studied in several epitaxial samples. In the case of (001) systems, phases remain constant for the long period oscillation, but for the short period oscillation they vary monotonically with the $d$-electron occupation number of the FM layers, at a rate of about 1.5 Å/electron. In the case of (110) systems the variation is nonmonotonic. A framework is presented with which the above observations can be understood.